1. Field of the Invention
The present invention relates to a hydraulic machine such as a hydraulic turbine, a pump and a reversible pump-turbine. More specifically, the invention relates to a hydraulic machine which can be easily disassembled and assembled.
2. Description of the Prior Art
A typical hydraulic machine, such as a hydraulic turbine and a pump, is installed in a double-flooring type building or a barrel type building. FIG. 15 shows a conventional hydraulic machine installed in a barrel type building. This hydraulic machine comprises a spiral case 1 connected to a steel pipe which introduces water from an upper pond (not shown), a stay vane 2a arranged on the inner periphery of the spiral case 1, and a stay ring 2 which clamps the stay vane 2a from the upper and lower sides to form a passage. The stay ring 2 has an upper flange 2b and a lower flange 2c. On the stay ring 2, a head cover 3 having a head-cover flange portion 3a is mounted by connecting the head-cover flange portion 3a to the upper flange 2b by means of bolts. In addition, on the stay ring 2, a bottom cover 4 having a bottom-ring flange portion 4a is mounted by connecting the bottom-ring flange portion 4a to the lower flange 2c by means of bolts.
In the passage inside of the stay vane 2a and between the upper cover 3 and the bottom cover 4, a guide vane 5 is arranged so as to form a circular cascade. The guide vane 5 has an upper spindle 5a and a lower spindle 5b. The upper spindle 5a of the guide vane 5 is rotatably supported on an upper guide vane bushing 6 and an intermediate bearing 7, which are provided on the head cover 3. The lower spindle 5b is rotatably supported on a lower bearing 8 provided on the bottom cover 4. Water flow-regulated by the guide vane 5 flows into a runner 9, and water flowing out of the runner 9 passes through an upper draft tube 10 to be discharged from a draft tube liner to a tailrace. The runner 9 is connected to the lower end portion of a turbine main shaft 11. Rotational torque of the runner 9 is transmitted to a generator via the turbine main shaft 11 to generate electricity. The head cover 3 is formed with an outer-periphery seal on the side of a runner crown 9a. The head cover 3 is also provided with a guide vane arm 12, a guide vane ring 13 and a operating ring 14. Above the stay ring 2, a lower pit liner 15 and an upper pit liner 16 are provided to form a pit of the hydraulic turbine. As shown in FIG. 16, each of the pit liners 15 and 16 is provided with a concreted turbine barrel 17. This turbine barrel 17 is designed to sufficiently support thereon the weights of generator stationary and rotary portions loaded on the lower pit liner 15, the hydraulic thrust weight when being driven, and so forth. The size of a turbine room 19 is determined in view of the size of the turbine barrel 17 and the maintenance space for auxiliary machinery provided in the turbine room 19. In the hydraulic machine with the aforementioned construction, particularly in a generator for a large capacity of reversible pump-turbine, a generator lower bearing bracket is provided with a thrust bearing and a lower guide bearing. In order to enhance the rigidity of the generator lower bearing to prevent the deformation thereof if thrust weight is applied thereto, it is required to decrease the diameter of the generator lower bearing bracket. In order to decrease the diameter of the generator lower bearing bracket, the inner diameter of the upper pit liner 16, on which the lower bearing bracket is mounted, must be decreased.
Therefore, in conventional hydraulic machines, the head cover 3, which is a large structure of the hydraulic machine and which is required to be disassembled for maintenance, has a four-piece structure which can be divided into four pieces. In addition, the inner diameter of the upper pit liner 16 is determined to be a necessary and minimum size in which each divided pieces can be lifted. For that reason, the inner diameter of the upper pit liner 16 is less than the inner diameter of the lower pit liner 15. As mentioned above, the conventional head cover 3 has a four-piece structure. Therefore, in order to assemble the head cover 3, four pieces must be combined with each other on the guide vane 5 in a complicated process to fasten joint portions by means of bolts, and then, the fastened four pieces must be mounted on the upper spindle 5a of the guide vane 5. The head cover 3 must be assembled at a high level above the guide vane 5 and within a narrow pit while the heavy equipment is lowered through the narrow upper pit liner 16 by means of a crane. Therefore, the assembly work must be carefully performed by skilled persons for several days.
In a field assembly of a hydraulic machine, in order to align the stationary parts, the head cover 3 is first temporarily assembled to perform the alignment. After the temporary assembly and alignment are completed, the head cover 3 is disassembled to be lifted. Thereafter, the runner 9 and the turbine main shaft 11 are introduced, and then, the head cover 3 is assembled again to install the hydraulic machine on the site. For that reason, it takes about two weeks to perform the assembly, disassembly and re-assembly processes of the head cover 3. However, in recent years, in the field installation work, it is required to shorten the processes to early increase the quantity of power supply, so that it is greatly desired to shorten the assembly operation of the head cover 3.
In addition, since the head cover 3 is divided into four pieces, the number of days for manufacturing the head cover is 1.5 times as longer as that of an integral head cover, the cost thereof increases, and the structural strength thereof becomes weak. The outer diameter of the turbine barrel 17 is derived by adding, to the inner diameter of the lower pit liner 15, a necessary thickness of concrete, which can bear the weights of stationary parts and rotary portions of the generator, and the water thrust load produced when the hydraulic machine is actuated. The inner diameter of the lower pit liner 15 is greater than the outer diameter of the head cover 3 by a work space required for tools which fasten head-cover mounting bolts. Therefore, the outer diameter of the turbine barrel is increased, so that the maintenance space for auxiliary machinery on the turbine room floor is insufficient. In some cases, the floor size may be increased to increase the construction cost. In addition, as mentioned above, since the head cover 3 must be disassembled and assembled after it is temporarily arranged on the guide vane 5, it is required to secure a space in a vertical direction for arranging therein the divided pieces of the head cover 3. Therefore, the height of the lower pit liner 15 is so defined as to secure the space. The installation position of the generator is determined on the basis of the height of the lower pit liner 15. Therefore, even if the height of the generator is decreased and the height of the building is also decreased, it is not possible to lower the installation position of the generator unless the method for assembling the head cover 3 is changed, so that it is not possible to decrease the construction period and cost.
In addition, since the installation position of the generator is a high position, the turbine main shaft 11 and the generator shaft are long, so that the critical speed is decreased. Therefore, it is required to enhance the rigidities of the shafts, e.g., by increasing the diameters of the shafts. Moreover, in a hydraulic machine, it is required to repair the runner 9 and the guide vane 5 due to cavitation damage and sedimentary friction while being actuated. When the runner 9 and the guide vane 5 are carried out for repair, it is required to disassemble the generator to lift the disassembled generator. Therefore, it is also required to disassemble a set of parts mounted on the head cover 3, so that the term of repairing work is remarkably increased. In particular, in recent years, as the capacity of the hydraulic machine is increased and the size thereof is decreased, the repairing interval is decreased due to cavitation damage and sedimentary friction, so that it is required to decrease the term of repairing work in order to improve the availability.